The diagram below shows how we can expand the sub-process seen in the previous diagram to explore how the individual activities and events interact with the Black-Box Pools.

It is important to note that the sub-process begins with a none start event, that is a plain circle, as the sub-process is triggered by the sequence flow coming into it. Sub-processes are never triggered by a catching event.

Sub-processes, on the other hand, can include throwing events, and we will see examples of this later.